In area charts, you can use symbols (circles, triangle, squares, and diamonds) to represent data points.
Select a data series (area shape), click Inspector in the toolbar, click the Chart inspector button, and then click Series.
Choose a symbol from the Data Symbol pop-up menu.
Adjust the size of the data point symbols by entering a value or using the stepper in the adjacent field.
Keynote provides other ways to customize area charts, including the following: